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Abstract

Thermal physiology of entomopathogenic nematodes (EPN) is a critical aspect of field performance and fitness. Thermal limits for survival and activity, and the ability of these limits to adjust (i.e. show phenotypic flexibility) depending on recent thermal history, are generally poorly established, especially for non-model nematode species. Here we report the acute thermal limits for survival, and the thermal acclimation-related plasticity thereof for two key endemic South African EPN species, Steinernema yirgalemense and Heterorhabditis zealandica. Results including LT50 indicate S. yirgalemense (LT50 = 40.8±0.3°C) has greater high temperature tolerance than H. zealandica (LT50 = 36.7±0.2°C), but S. yirgalemense (LT50 = -2.4±0°C) has poorer low temperature tolerance in comparison to H. zealandica (LT50 = -9.7±0.3°C), suggesting these two EPN species occupy divergent thermal niches to one another.

Acclimation had both negative and positive effects on temperature stress survival of both species, although the overall variation meant that many of these effects were non-significant. There was no indication of a consistent loss of plasticity with improved basal thermal tolerance for either species at upper lethal temperatures. At lower temperatures measured for H. zealandica, the 5°C acclimation lowered survival until below -12.5°C, where after it increased survival. Such results indicate that the thermal niche breadth of EPN species can differ significantly depending on recent thermal conditions, and should be characterized across a broad range of species to understand the evolution of thermal limits to performance and survival in this group.

Author Comment

This submission has been accepted at PeerJ.

Supplemental Information

Acclimation and lethal thermal tolerances for two species of entomopathogenic nematodes, Heterorhabditis zealandica and Steinernema yirgalemense

Additional Information

Competing Interests

Author Contributions

Matthew P Hill conceived and designed the experiments, performed the experiments, analyzed the data, wrote the paper, prepared figures and/or tables, reviewed drafts of the paper.

Antoinette P Malan conceived and designed the experiments, contributed reagents/materials/analysis tools, wrote the paper, reviewed drafts of the paper.

John S Terblanche conceived and designed the experiments, analyzed the data, contributed reagents/materials/analysis tools, wrote the paper, reviewed drafts of the paper.

Data Deposition

The following information was supplied regarding the deposition of related data:

Datasets for this study are available on FigShare:

http://dx.doi.org/10.6084/m9.figshare.1356153

http://dx.doi.org/10.6084/m9.figshare.1356152

http://dx.doi.org/10.6084/m9.figshare.1356151

http://dx.doi.org/10.6084/m9.figshare.1356150

Funding

Funding for this research was provided to JST through Hortgro grant US-APE-NTT-2013-01. JST and AM are also supported by the National Research Foundation THRIP award and Incentive Funding for Rated researchers. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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